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Trusses Vs. Rafters For Load Bearing—Pros, Cons, & Major Differences

Are you doing a re-roofing project, and do you want to know whether trusses are better at bearing load than rafters or vice versa? You’ve come to the right place, for we have researched this question, and we have the answer for you.

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Roof trusses are cheaper, less labor intensive solution, yet structurally stronger than roof rafters when it comes to supporting a load. With trusses, you'll get an accurate, fast installation using an eco-friendly method.

However, roof raftors are the traditional framing method and you'll gain attic access with this technique. Yet rafters are susceptible to warping, are less eco-friendly, and do take considerably more time to build. 

Let’s talk more about trusses and rafters in the succeeding sections. Learn more about the advantages and disadvantages of each so you can decide for yourself which one is more appropriate for your roofing project.

Read on!

Wooden roof truss being lifted by a boom truck forklift in the roof, Trusses Vs Rafters For Load Bearing—Pros, Cons, & Major Differences

 

What is the purpose of roof framing?

The roof framing is the part of your house that supports the weight of the external roofing components like the roof deck or the roof cladding. It is the part of your house that supports the weight of shingles or roof tiles that you plan to install later.

It is a three-dimensional structural framework that is made of a system of beams in specific angles and positions to provide the necessary support for your roof.

What is the purpose of roof framing - Home new wood frame stick built home under construction a blue sky

Although roof framing is mostly made from lumber, you can also use metal, albeit it would cost more. However, a metal roof framing would be much stronger than a wooden frame.

Even though the core of a roof frame is made from trusses or rafters, designing a roof frame is not this simple. You need to build a different type of roof framing for each type of roof that you want to use.

What is a roof truss?

What is a roof truss - trusses just placed atop a house under construction.

A roof truss is a structural weight-bearing frame that bridges the distance across a space like in a house. It has a characteristic look that combines several triangles into a single framework.

A roof truss design follows the concepts of tension and compression. Engineers design each component lumber of a roof truss carefully, using precise measurements to maintain the relationship between the forces of tension and compression within the roof truss design.

Some components of the triangles handle compressive forces applied on the truss, while other components handle tensile forces.

External diagonal forces are broken into vertical and horizontal components. Each roof truss component handles a specific force component. This creates a force distribution system that effectively maximizes the material strength of the roof truss.

This force distribution system allows a roof truss to span a large area of the house without the need for support from below.

See how trusses are constructed in the video below: 

What is a roof rafter?

What is a roof rafter - Attic space in newly-built house, ready for conversion. Wiring has been done.

A roof rafter is a structural component of the roof. One end goes to the ridge board, while the other end goes to the wall plate of an external wall.

Rafters are installed side by side with a specific distance between each one. They can be made from lumber or steel.

The installation and distribution of rafters over the wall plate allow it to distribute the load to the wall.

Roof rafters can only support the roof over a limited distance. Increasing this distance without adding support under the rafter requires that you increase the width of the rafters.

Modern rafter designs incorporate some of the truss concepts above to improve the amount of weight that it can support.

What are the advantages of roof trusses?

Perhaps the biggest advantage of a roof truss is that it is built offsite in a truss plant.

When doing a roofing project, a contractor will provide the truss plant with the dimensions of the roof trusses that the project needs. A roof truss designer will enter those measurements into the software that will help design the roof truss.

Saws run by the computer will make precise cuts on lumber for the truss. Because a computer guides the saws that cut the lumber, there is very little waste, making the entire truss assembly fast and efficient. This reduces the cost of waste disposal and losses from waste. And this makes roof trusses eco-friendly because it does not waste wood.

  • Each roof truss is made specifically for the roof of your home. The efficiency makes trusses cheaper than rafters. And the efficient manufacturing process allows roof trusses to use up to 40% less wood than rafters.
  • The computerization of measuring and cutting makes everything more accurate. This means that each roof truss that you receive will have the exact same dimensions.
  • Some truss plants operate twenty-four hours each day of the week to fill up the roof truss orders fast.
  • Another major advantage is that trusses can provide roof support over a larger area. This allows you to have any shape for your rooms. Place rooms where you want to, not where you need to.
  • You can also install roof trusses faster than roof rafters. Additionally, it is easier to install, which means you need less skilled labor, reducing the total cost of construction.
  • A roof made of roof trusses can extend the effective life of your house. It provides better support against wind, rain, and snow because of its ability to bear forces and distribute them.

What are the advantages of roof rafters?

What are the advantages of roof rafters - Beautiful sturdy wood Architecture.

Building a roof using roof rafters or stick framing is the traditional method of building a roof for houses. Unlike roof trusses, traditional roofers measure, cut, and assemble roof rafters on site. Thus, you can find more people who know how to build roof rafters.

Rafters give you a larger space available for the attic.

What are the disadvantages of roof trusses?

The strength of roof trusses relies on a network of diagonal and horizontal beams that provide compression and tension support. This network of beams takes up space. This means that you can no longer have a room in the attic if you use roof trusses.

Termites and warping are a disadvantage that is common to any wooden structure.

What are the disadvantages of roof rafters?

Building roof rafters requires a lot of work hours, making labor costs expensive. Building roof rafters requires more materials to build equivalent support that roof trusses can provide. This makes the material costs more expensive too.

  • Roof rafters do not use software for measurements, and this makes it less accurate and efficient. Lower efficiency means that roof rafters produce more waste and are not eco-friendly.
  • It takes a longer time to build roof rafters because roofers do everything manually.
  • Wooden roof rafters are also vulnerable to warping and termites.

Can you use WPC for roof trusses?

Yes, you can use WPC or wood plastic composite for roof trusses.

WPC is a hybrid material that combines the advantages of wood and plastic. It is made from a blend of wood fiber, wood flour, thermoplastics, inorganic fillers, and plastic composites. Recycled thermoplastics are a common component of WPC.

Because it is a hybrid of wood and plastic, it is a water-resistant material, and it can resist climatic conditions. It resists the effects of chemicals and fire.

WPC trusses are also very easy to maintain. It doesn’t attract insects and small animals, making it safe from damage from these two. WPC is also resistant to hot summer conditions, making it ideal for outdoor use.

What is a truss plate?

What is a truss plate - Detail of a truss with galvanized nail plates.

The different components of a roof truss are not held together with nails or screws. Instead, truss plants use truss plates to keep the parts of a roof truss together.

A truss plate is a piece of flat metal that has holes. Under each hole is a sharp nail-like protrusion. This sharp protrusion is made from the material that they punched from the plate to create the hole.

Truss plants install a truss plate on both sides of two or more roof truss components. A machine presses the truss plates on both sides of the truss components where they meet.

A worker will hammer the truss plate on one end to keep it in place. Once all the truss plates are in place, a large machine will roll over the roof truss assembly to apply an even force on the plates and drive them more firmly into the wood.

The size of the truss plate to use for a roof truss connection depends on the width of the member timbers. Thus, truss plates come in different sizes.

Pronged Truss Plate is available on Amazon through this link.

How much weight can you hang from a roof truss?

Truss designers follow the local building code when designing your roof truss on their computers. This means that the weight capacity of a roof truss is dependent on the local building code at your place. Local building codes commonly follow the IRC or the International Residential Code.

You can increase the weight capacity and include this in the computations that you will give the roof truss designer so that you will get the truss load capacity that you want. The average weight that a roof truss should be able to support is 40 pounds per square foot. This can be higher or lower in your area, depending on the building code.

This is the weight that a roof truss can support by hanging it on its horizontal beams.

Conclusion

Roof trusses can support more weight than roof rafters, yet you'll gain additional attic space with rafters. Trusses are the more affordable option and less labor intensive. But, if you're looking for craftsmanship, hand-building the rafters is the 'ol fashioned method of framing.

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